Abstract
The hen harrier is a heavily persecuted bird of prey in Great Britain since its diet includes Red grouse, a game bird shot in driven and walked-up grouse shooting. Unlike walked-up shooting where shooters walk up moors and flush grouse with dogs, in driven grouse shooting the grouse are driven by beaters towards static shooters. Driven grouse moors (DGMs) are increasingly being managed to sustain high densities of Red grouse intensifying a long-standing conservation conflict between conservationists and grouse moor keepers. A metabarcoding approach was used with degenerate universal cytochrome oxidase I and cytochrome b primers along with hen harrier blocking primers. A novel sampling method was used to detect prey in buccal swab samples from chicks from broods across Great Britain from both managed and unmanaged moorland habitats. This resulted in detection of 62 species of prey across 51 broods with Meadow pipit, Red grouse, Wren, Skylark, and voles being most frequently detected. Frequency of occurrence data and species accumulation curves reveal high incidence of Red grouse and low prey species richness in the diet of hen harriers in DGMs but low incidence of Red grouse and high prey species richness in walked-up and unmanaged moors. Waders were only detected within walked-up and unmanaged moors and not within DGMs where they have been reported to occur at high densities. Regional species detected included endemic species such as the Orkney vole seen only in Orkney. This study represents the first metabarcoding-based dietary analysis in a raptor using buccal swabs.
Highlights
The hen harrier (Circus cyaneus) is a raptor species with a wide distribution in the northern hemisphere
We have shown for the first time that non-invasive buccal swab samples from chicks can be used successfully for identification of prey species in birds
Buccal swab samples have several advantages over faeces, the most commonly used non-invasive sample for DNA based diet analysis e.g. (1) fewer PCR inhibitors are co-extracted with DNA, (2) there is less chance of contamination from environmental DNA, (3) DNA undergoes less degradation than in faecal samples which could have been deposited long before the sample was taken, and (4) the study species is directly known whereas identification of faecal source can sometimes be difficult (Morin et al 2016)
Summary
The hen harrier (Circus cyaneus) is a raptor species with a wide distribution in the northern hemisphere. Red grouse are shot in large numbers in driven grouse shooting during the shooting season, with an average of 72 brace (144 birds) per day of shooting (Sotherton et al 2009) This type of grouse shooting where grouse are driven by beaters towards the shooters requires the grouse population to be far higher than would naturally occur e.g. 5.6–7.74 willow grouse (Lagopus lagopus) per km have been reported in unmanaged habitat in Sweden by Willebrand et al (2011) and 104.9 Red grouse per km have been reported in driven grouse moors (DGMs) in northern England by Robertson et al (2017). An alternative form of grouse shooting, walked-up shooting, involves shooters walking up moors and shooting grouse that are flushed using dogs This form of grouse shooting, practised in Wales, is less intensive in its management practices and results in far smaller numbers of grouse being shot (Sotherton et al 2009)
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